This invention relates to an improved slip assembly for hanging an elongate member within a wellbore, and more particularly, for hanging a liner within a well casing in the wellbore.
Conventionally, a liner or similar elongate member is hung by means of a slip assembly comprising wedge shaped slip elements received in circumferentially spaced relation about the member, each slip element having teeth about its outer side and a downwardly and inwardly conically shaped inner side for sliding over a correspondingly shaped frusto conical wedge surface on the outer side of the member.
The slip elements are held in retracted position, as the liner is lowered into the casing until reaching a desired depth, and then, when so positioned, caused to move over the frusto conical surface of the member so to cause its teeth to grip the casing. When the casing is so gripped, the weight of the liner is slacked off onto the slips in order to transfer the load of the liner to the casing.
One problem with a conventional slip assembly of this type is the need to coordinate the setting of the individual slips so that teeth thereof engage the outer casing substantially simultaneously. Also, it is of course costly to machine multiple wedge surfaces about the liner, as well as to provide multiple slip elements, and it is the principle object of this invention to provide a slip assembly for this purpose which requires only a single slip element cooperable with only a single wedge surface of the liner or other elongate member.
This and other objects are accomplished, in accordance with the illustrated and preferred embodiment of this invention, by well apparatus which comprises an elongate member adapted to be lowered into and suspended within a wellbore and having a frusto conical surface thereabout, and a circumferentially expandible and contractible, wedge shaped c-ring having slip teeth about its outer side and a frusto conical surface on its inner side. The outer surface of the c-ring is adapted to be installed about the frusto conical surface of the elongate member for sliding between a contracted position, in which the member is free to vertically move in the wellbore, and an expanded position in which the slip teeth engage the wellbore, whereby the weight of the member may be slacked off to hang it from the casing. The member has a recess to receive an end of the c-ring and thus retain the slip in contracted position, and a means is carried by the member for removing the end of the ring from the recess so as to permit the ring to expand as is slides over the conical surface to cause its slip teeth to engage and bite into the wellbore so that the weight of the member may be slacked off onto the casing.
In the illustrated embodiment of the invention, the frusto conical surfaces of the member and slip extend downwardly and inwardly, the lower end of the slip is received in an upwardly facing recess in the member, and the teeth of the c-ring face downwardly in position to engage the wellbore, as the c-ring is raised over the surface of the member whereby the member may be suspended within the wellbore. The means for raising the lower end of the c-ring from the recess to a position for sliding along the conical surface of the member comprises at least one tie bar extending vertically through the member for guided reciprocation with respect thereto. More particularly, the inner side of the c-ring and lower end of the tie bar have interfitting parts which enable the lower end of the c-ring to be raised out of the recess, but which are disengageable when the bar is raised to permit the ring to expand into engagement with the wellbore.
Preferably and as illustrated, the inner frusto conical surface of the c-ring has relatively blunt teeth about its frusto conical surface for engagement with the frusto conical surface of the member so as to control the friction between them, and thus control the applied to the casing.